<!doctype html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style type="text/css">
		.box{
			margin: 100px auto;
			width: 200px;
			height: 100px;
			background: red url() 0 0 no-repeat;
			color: #fff;
			font-size: 40px;
			text-align: center;
			line-height: 100px;
		}

	</style>

	<script type="text/javascript">
		window.onload = function  () {
			
			btn = document.getElementById('btn');
			box = document.getElementById('box');

			btn.onclick = function  () {
				time = setInterval(run,1000)
			}
			num=60;
			function run () {
				box.innerHTML=num;
				if(num==0){
					clearInterval(time);
				}
				num--;
			}


		}
	</script>


</head>
<body>
	<input type="button" value="点我吧" id="btn">
	<div class="box" id="box">
		<div class="son"></div>
	</div>
	<div class="span">
		<div class="son1"></div>
	</div>
</body>
</html>